(a) Field of the Invention
The present invention relates to an exposure mask and a method of divisional exposure.
(b) Description of Related Art
A display device, such as a liquid crystal display (LCD), includes a plurality of pixels arranged in a matrix, and each pixel includes a transparent pixel electrode for displaying images. The pixel electrodes are driven by signals from signal lines, including gate lines and data lines, that intersect each other to define pixel areas and are connected to the pixel electrodes through switching elements such as thin film transistors (TFTs). The switching elements control data signals from the data lines in response to scanning signals from the gate lines.
The LCD includes a TFT array panel including the signal lines, the pixel electrodes, and the TFTs, and a common electrode panel including a common electrode facing the pixel electrodes and a black matrix having openings facing the pixel areas.
When an active area on a backplane for LCDs is too large to use an exposure mask, the entire exposure is accomplished by repeating a divisional exposure called a “step-and-repeat” process. One divisional exposure unit or area is called a “shot”. Since transition, rotation, distortion, and other problems are generated during light exposure, the shots may not be aligned accurately. Accordingly, parasitic capacitances generated between wires and pixel electrodes can differ depending on the shots, thereby causing a brightness difference between the shots which is recognizable at the pixels located proximate a boundary between the shots. Therefore, a “stitch” defect is generated on the screen of the LCD due to brightness discontinuity between the shots.
It has been suggested that boundaries of the shots be made saw-toothed or that several unit stitch areas be selectively subjected to light exposure simultaneously in order to reduce the stitch defect. However, the misalignment between adjacent shots is not effectively removed, and in addition, the misalignment in a direction perpendicular to a moving direction of an exposure mask is not solved.